Chemical process for splitting of ethylidene diacetate



atenied ea. 2, 19411 CHEIVHCAL PROCESS FOR SPLITTING'OF I ETENE DIACETATE Frank 0. Cockerille, Waynesboro, Va., assignor to E. ll. du Pont de Ncmours & Company, Wilmington, DeL, a corporation of'Delaware No Drawing. Application March 4, 1939, Serial No. 259,796

I 6 Claims. (Cl. 26il549)v This invention relates to the splitting of ethylidene diacetate to form acetaldehyde and acetic anhydride.

The method described in U. S. Patent No. 1,579,248 of splitting ethylidene diacetate in the presence of zinc halide as a catalyst to form acetic anhydride and acetaldehyde, while conducive to high yields of the desired products,

leads to the formation of considerable quanti-' ties of valueless tarry icy-products. These ccnstitute a corresponding waste of the ethylidene diacetate, and their removal leads to waste of catalyst.

It has been discovered that it ispossible to greatly reduce the, amount of tar. formation and to efiect a very substantial saving in starting material and catalyst by adding to the ethylidene diacetate in a splitting vessel certain compounds which in themselves have negligible splitting activity but which serve to modify, or modulate, the tar-forming action of the regular catalyst.

It is, therefore, an object of this invention to provide an improved process for splitting ethylidene diacetate. Another object 'is to provide a process for splitting ethylidene diacetate-that is saving of the catalyst and the diacetate. A still further object of the invention is to reduce the formation oftarry by-products in the ethylidene diacetate splitting still without inhibiting the rate of splitting. Other objects will be apparent from the description which follows.

The objects of this invention are accomplishedby splitting the ethylidene diacetate in the presence of a zinc halide catalyst and a stable zinc derivative of an organic compound that is soluble in the reaction mass. Such a zinc derivative of an organic compound will not substantially reaction mass by reason of the presence therein of the zinc halide and the zinc derivative of an organic compound. The expression zinc complex organic compound" will, hereinafter, be used to specifically embrace the zinc halide-zinc organic radical complex compound and/or halide zincorganic radical complex compound.

. not suitable, for they are converted to zinc aceinhibit the rate of the splitting reaction. The

said zinc derivative of an organic compound may be added as such or.may be formed'in situ in the reactionmass by the addition ofan organic compound and a zinc salt., There is also evidence of the formation, within the reaction mass, of a zinc halide-zinc organic radical complex compound (ZiiHalaZnR), or a halide-zinc-organic radical complex compound (HalZnR).- In the formulas Hal designates a halogen atom and 13. designates an organic radical other than a carboxylate. in the claims, the expression splitting ethylidene diacetate in the presence of a zinc halide catalyst and a zinc derivative of an organic compound is intended to include the splitting of the ethylidene diacetate in the presence of a zinc complex organic compound formed in situ in the In the following description, andtate and the anhydride of the higher acid. In addition to stability as an essential requirement of satisfactory zinc derivatives for use in accordance with this invention, the modifier must also beef sufficient solubility that a concentration of about 1 mol thereof per mol of zinc halide may be used. A solubility greater than this specified value is desirable, since it may be advantageous to build up a.concentration of modifier which is greater than equimola r to the halide. Such a modifier will not seriously inhibit the rate of splitting. v

The zinc derivatives are generally best prepared in situ from the equivalent amount of zinc oxide or acetate and a slight excess of the acidic substance, although, if desired, the zinc derivative can be added to,the still along with the other materials. Where the zinc is added in theform of its acetate, the new zinc derivative is formed by thermal displacement ofthe acetic acid from the zincacetate. J Organic compounds containing an acidic hydrogen atom bound directly to carbon or nitrogen which will react with a zinc compound to form zinc derivatives that are soluble in the reaction mass and not volatile or subject to decomposition in the reaction mass are especially useful for the formation of the zinc derivative of an organic compound. Such organic compounds having an acidic hydrogen atom in which the zinc replaces said acidic hydrogen atom maybe selected from the following classes of organic compounds:

1. Primary or secondary amides or ammonium salts in which the acidic radicals may be of either aryl, aralkyl, simple alkyl, or naphthenic derivation. I

2. Mono-acylated or arylated primary amines.

3. High-boiling secondary amines containing substituent groups of such negativity as to prevent acetylation of the free amino hydrogen in the reaction mass.

4. Compounds which contain acidic methylene or methine groups.

5. Substituted phenols, particularly those in which the positions ortho and para to the hydroxyl group are substituted with electro-positive groups, such as the nitro group.

As specific organic compounds which may be used inaccordance with the present invention for the formation of zinc derivatives the following may be mentioned: Phthalimide, triphenylmethane, acetamide, urea, diphenyl methane, fiuorene, acetanilide and dixylenol methane have proved satisfactory from the standpoint of stability and solubility, are effective in reducing tar formation, and do not substantially retard the rate of splitting. Other compounds which may form suitable zinc derivatives and which may be used in accordance with this invention are thiourea and substituted thioureas, cyanamide and its polymers, dicyandiamide and melamin, guanidine and substituted guanidines, cyanuric acid, hydrazobenzene, as-diphenyl hydrazine, aryl sulfonamides, alkyl sulfonamides, picric acid and other high-boiling phenols, uric acid and other purines, barbituric acid, thiophenols and mercaptans. It is to be understood, of course, that such zinc organic compounds have the required stability, solubility and freedom from any substantial inhibition in the rate of splitting of the ethylidene di- Example I The flask is charged with 500 grams of purified ethylidene diacetate, 3.8 grams of zinc acetate, and 9.4 grams of phthalimide. The temperature of the ingredients is raised to 150 C., whereupon 3.6 grams of zinc bromide are added. At this stage it is observed that all the substances are in solution. Aldehyde and anhydride are taken off at the top of the column and fresh ethylidene diacetate-is added at a rate suflicient to maintain the original level in the splitting flask. The anhydride and aldehyde are separated by fractional distillation. In order to maintain continuously the formation of anhydride and aldehyde, it is necessary to purge from 2 to 10% of thecontents of the splitting vessel at intervals of one hour or more, and to add ethylidene diacetate, catalyst and modifier to replace that which has been removed by purging.

In the absence of the modifier the purge rate is about three times as great as when the above conditions are observed; hence, about three times as much catalyst is required for the same production of anhydride and aldehyde. In either case the principal loss in yield is the formation of tarry material, the extent of this loss being measured by the purge rate required for satisfactory splitting.

Example II grams) replaces the phthalimide. The yield of anhydride and aldehyde is practically the same as when the zinc derivative of phthalimide is used as the modifier.

Example III The flask is charged with 500 grams of technical ethylidene diacetate, 1.0 gram of zinc oxide, and 2.6 grams of acetamide. When the temperature of these substances has been raised to approximately C., 2.4 grams of zinc bromide (or 1.5 grams zinc chloride) are added. The production of anhydride and aldehyde is efiected in the manner described in Example I. The rate of splitting is somewhat lower than Example I. A somewhat lower purge rate may be maintained due to the lower concentration of the splitting catalyst; hence, the yield of desired products is somewhat higher in terms of catalyst consumed.

Example IV Splitting is conducted in a manner entirely similar to that described in Example III, except that urea (1.2 grams) is substituted for the acetamide. The results are identical with those obtained in Example III.

Although the modifiers included in this invention do not seriously affect the activity of the catalyst insofar as splitting is concerned, they do largely prevent the undesired formation of tar. This behavior is believed to be in line with the observation that the presence of a modifier in the splitting mixture prevents a major portion of the loss of volatile halogen derivative which may be observed in its absence. It is reasonable to suppose that the formation of tar may be caused by these volatile halogen deratives, and that the presence of excess zinc m soluble but neutral form either exertsa mass-action effect in repressing the formation of the volatile halogen compound (by some phenomenon related to hydrolysis) or else acts as a buffer in neutralizing the acidic halogen derivative immediately after its formation. Whatever may be the phenomena, the net result is that the neutral zinc derivative prevents the undesirable side reaction without seriously decreasing the rate of formation of anhydride and aldehyde, so that with the use of a modifier it is possible to decrease severalfold the amount of tar produced and to greatly decrease the amount of catalyst required in split- -ting the same amount of ethylidene diacetate.

Throughout the discussion of this invention the splitting catalyst specifically employed has been zinc bromide or a complex salt containing zinc bromide. It is to be understood that other zinc halides, for instance zinc chloride and zinc iodide, may be used to good advantage.

As the result of this invention, the splitting of ethylidene diacetate may be carried out much more efficiently with the purge rate reduced to one-third, or even less, than used heretofore, and

with substantially proportional savings of the catalyst, and very substantial reductions in the loss ofacetic acid values. Another advantage of this invention is that the use of these modifiers permits the use of a higher concentration of splitting catalyst than has hitherto been considered advisable, since in the presence of the modiher the formation of tar is but little more than proportional to the concentration of the splitting catalyst.

Obviously, many modifications and changes may be made in the above-described details without departing from the nature and spirit of the invention, and it is to be understood that it is not to be limited to the speciiic description excent as set forth in the appended claims. I claim: 7 1. The process of splitting'ethyiidene diacetate to form acetaidehyde and acetic anhydride which comprises splitting the ethylidene diacetate by heating in a liquid reaction mass containing a zinc halide catalyst and a tar-formation inhibiting modifier, said modifier consisting of a zinc derivative. of an organic compound having an acidic hydrogen atom in which the zinc replaces said acidic hydrogen atom and which zinc derivative is stable and soluble in the liquid reaction mass to the extent of at least one moi for each moi of zinc halide present in the reaction mass.

3. The process of splitting ethylidene diacetate by heating to form acetaidehyde and acetic anhydride which comprises splitting the ethyiidene diacetate in a liquid reaction mass containing a catalyst comprising a zinc complex organic compound consisting of the'reaction productoi a zinc halide compound and an organic compound having an acidic hydrogen atom in which zinc replaces said acidic hydrogen atom and which zinc complex organic compound is stable and soluble in the reaction mass.

4. The process of splitting ethylidene diacetate by heating to form acetaidehyde and acetic anhydride which comprises addingto the liquid reaction mass of ethyiidene diacetate a zinc halidecatalyst, zinc acetate and phthalimide.

5. The process 01 splitting ethylidene diacetate by heating to form acetaidehyde and acetic anhydride which'comprises adding 'to the liquid reaction mass of ethyiidene diacetate a zinc halide catalyst, zinc acetate and triphenylmethane.

6. The process of splitting ethyiidene diacetateby heatingto iorm acetaidehyde-and acetic anhydride which comprises adding to the liquid reaction mass of ethylidene diacetate a zinc halide catalyst, zinc oxide and urea.

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